Thin organic coatings on substrates have important utility in electronic and optical devices such as photovoltaic cells, xerographic photoreceptors, gate-controlled diodes, field effect transistors, gas detectors, information storage devices, optical light switches and light modulators, and the like.
An important objective in the application of thin films to substrates is the formation of a continuous film which has uniform thickness and is free of defects and microporosity.
One preferred method of applying thin films to substrates involves the use of the Langmuir-Blodgett technique.
The Langmuir-Blodgett technique is reviewed in J. Macromol. Sci.-Rev. Macromol. Chem., C21(1), 61(1981); incorporated herein by reference.
An extensive elaboration of Langmuir-Blodgett technology is published in Thin Solid Films, Vol. 99(1983), which includes papers presented at the First International Conference On Langmuir-Blodgett Films, Durham, Great Britain, Sept. 20-22, 1982; Elsevier Sequoia S. A., Lausanne; and in
Thin Solid Films, Vol. 132-134 (1985) which includes papers presented at the Second International Conference on Langmuir-Blodgett Films, Schenectady, N.Y.; incorporated herein by reference.
In 1917 Irving Langmuir developed the experimental and theoretical concepts which underlie our understanding of the behavior of organic molecules in insoluble monolayers on the surface of water. Langmuir demonstrated that long-chain fatty acids on the surface of water form films in which the molecules occupy the same cross-sectional area whatever the chain length of the molecules. The films are one molecule thick, and the molecules are oriented at the water surface, with the polar functional group immersed in the water and the long nonpolar chain directed nearly vertically up from the water surface.
This understanding of the nature of insoluble monolayers was facilitated by the development of a surface balance, which is associated with Langmuir's name.
In 1919 Langmuir reported a development in which fatty acid monolayers on water surfaces were transferred to solid supports such as glass slides. In 1933 Katherine Blodgett announced the discovery that sequential monolayer transfer could be accomplished to form built-up multilayer films, i.e., unitary laminate structures now universally referred to as "Langmuir-Blodgett films".
Grunfeld et al in Thin Solid Films, 99, 249(1983) demonstrate the application of a Langmuir-Blodgett layer as a potentially useful integrated optics component by employing the optical absorption anisotropy of a diacetylene film in a polarization mode filter.
U.S. Pat. No. 4,584,235 describes the preparation of substrates coated with a thin film of a phthalocyanine compound for use as a component in electronic and photochemical devices.
There is increasing interest in the development of new and improved techniques for coating substrates with thin solid films which have the unique properties of Langmuir-Blodgett media for electronic and optical applications.
Accordingly, it is an object of this invention to provide an improved process for depositing a thin solid film on a substrate.
It is another object of this invention to provide a substrate with a surface coating of a continuous film which is uniform in thickness and is free of defects and microporosity.
It is a further object of this invention to provide a nonlinear optical medium which is composed of a transparent substrate which is coated with at least one monomolecular layer of oriented organic molecules which exhibit nonlinear optical susceptibility.
Other objects and advantages of the present invention shall become apparent from the accompanying description and Examples.